1. Field of the Invention
The present invention pertains to analyte detection and, more specifically, to the use of luminescent compounds for the detection of explosives, such as nitroaromatic-, nitramine-, nitrate-ester-, inorganic nitrate-, chlorate-, perchlorate-, bromate-, peroxide-, smokeless powder- and black-powder-based explosives.
2. Discussion of the Prior Art
Peroxide-based explosives packaged within improvised explosive devices (IEDs) are a mainstay for some terrorist groups around the world. Peroxides are highly sensitive to heat, shock, and friction, and are capable of causing substantial damage. Triacetone triperoxide (TATP) is one type of peroxide-based explosive typically used, because it may be prepared from household chemicals that are easy to obtain. Three other examples of peroxide-based explosives are hydrogen peroxide, HMTD (hexamethylene triperoxide diamine) and MEKP (methyl ethyl ketone peroxide). The primary factors affecting the growing use of peroxide-based explosives are twofold. First, techniques used to detect traditional nitrogen based high explosives such as trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX) and pentaerythritol tetranitrate (PETN) have shown impressive advancements in recent years, which make the use of these explosives riskier for terrorists. Second, regulation, lack of availability of military grade explosives and difficulty of production of source materials create situations where traditional explosives are not practical for some terrorist groups. These two factors provide the impetus for terrorists to adapt their destructive repertoire to include peroxide-based explosives. The progression seen in the Israeli conflict from using traditional high explosive IED's to peroxide based IED's underscores the urgent need to detect this class of dangerous explosives. Moreover, it highlights the necessity for innovative solutions to terror activities, which are constantly evolving and adapting. In addition, it would be advantageous to incorporate peroxide sensing into a system which would be capable of detecting multiple classes of explosives so as to provide quick and simultaneous detection of each.
Optical sensing methods are often desired for trace explosive screening because they can be packaged into simple-to-use, low-cost devices. In contrast, conventional detection methods, such as X-ray diffraction, nuclear quadrupole resonance, ion mobility spectrometry, and gas chromatography-mass spectrometry, though highly sensitive, are expensive, difficult to maintain; susceptible to false-positives, and are not easily manufactured into low-power, portable devices.
Colorimetric techniques are also known which can detect the presence of peroxides. One such method uses acids and potassium iodide which reacts with peroxides to yield a brown color or a blue color when also in the presence of starch. Strong acids are often required to decompose organic peroxides to hydrogen peroxide, the chemical often detected by the colorimetric reactions. Portable colorimetric chemical sensing kits have the value of displaying easily interpreted optical signals with fast response times. However, there remains a demand for explosives sensors which maintain the simplicity of use and interpretation found in colorimetric kits, but with improved detection sensitivities and reduced exposure to toxic or corrosive chemicals, such as the acids used in the method mentioned above. Other desirable attributes of the sensors would be a simple one-step detection technique for peroxides which may be packaged with optical detection methods for other explosives to yield screening devices capable of detecting a wide range of explosives quickly.
Inorganic nitrates, such as uronium nitrate (commonly referred to as urea nitrate), ammonium nitrate, and potassium nitrate, are common components of industrial, military, and homemade (e.g., pipe bomb) explosives. The rapid and sensitive detection of these compounds can therefore be used to identify possible explosive threats. Because inorganic nitrates are not highly volatile, solid state sampling techniques may be favored for their detection. Colorimetric techniques are available for the rapid and simple detection of inorganic nitrates which require a series of chemical transformations. These methods, however, have a number of disadvantages, including low sensitivity, high false alarm rates, and inconvenient analysis and clean-up procedures. In addition, these methods can often expose users to large quantities of chemicals through repeated wet-chemistry style sampling steps.
The present invention provides a method whereby both trace peroxide-based explosives and trace nitrogen-based explosives may be reliably detected without the disadvantages of the prior art.